Nanoparticle iron–titanium oxide aerogels

Nanostructured iron oxide–titania aerogel materials have been prepared by sol–gel polymerization of iron acetylacetonate with titanium butoxide and supercritical drying. Their structural properties, including particle morphology, crystalline phase, bond linkage and surface area, were varied by addition of ferric oxide into the titania matrix, as characterized by means of HRTEM, XRD, FT-IR and the BET method. X-ray photoelectron spectra (XPS) revealed a stronger interaction between iron and titanium atoms in the mixed oxide structure, thus influencing the surface dispersion of Ti3+/Ti4+ and Fe2+/Fe3+ redox pairs. The reactivity of the 8–40 nm aerogel particles was investigated with the catalytic oxidation of methanol at ambient pressure. Conversion and product selectivity were dependent upon iron dispersion, catalyst pretreatment and oxygen feed. Dimethyl ether was the most dominant product formed on all of the catalysts, indicating strong Lewis acid characters on the iron–titanium oxide surface. The dependence of ether formation activity loss on oxygen feed attenuation suggests that the mobile lattice oxide anions placed near to iron sites are more reactive to participate in the surface reaction and that oxygen molecules help to maintain the iron sites reduced during reaction in the high oxidation state for Lewis chemisorption. A good correlation between particle structures and catalytic properties is proposed.